1. Field of the Invention
The present invention relates to a method for controlling communication, a method for controlling a terminal, a communication control device, a gateway terminal, and a mobile terminal, and in particular, to a method for controlling communication, a method for controlling a terminal, a communication control device, a gateway terminal, and a mobile terminal all of which are used in a mobile communication network having a core network and an ad hoc network integrated together.
2. Description of the Related Art
With a radio ad hoc network technique (see, for example, Chairs: Joseph Macker and Scott Corson, “Mobile Ad-hoc Networks (manet), IETF working group, (retrieved on Oct. 4, 2004), Internet<URL: http://www.ietf.org/html.charters/manet-charter.html>), each mobile terminal serves as a router to autonomously constitute a radio network without using a core network so that data can be transmitted and received via another mobile terminal. The radio ad hoc network does not require any core network and is thus helpful in temporarily constructing a network or taking measures for a disaster.
Instead of allowing each mobile terminal in the radio ad hoc network to communicate using another mobile terminal, other techniques allow the mobile terminal to connect to a global network via a core network or to communicate with another terminal via the core network (see, for example, U. Johnson et al., “MIPMANET-mobile IP for mobile ad hoc networks,” IEEE MobiHOC, pp 76-85, 2000 and R. Wakikawa et al., “Global Connectivity for Ipv6 Mobile Ad Hoc Networks” (draft-wakikawa-manet-globalv6-02.txt), Internet Draft, IETF, November 2002). These techniques enable a mobile terminal to transmit a signal to a terminal in the core network, while enabling the terminal in the core network to transmit a signal to the mobile terminal. This can be accomplished when a mobile terminal having a specific address retrieves a node or terminal that serves as a gateway to the core network so that the node can provide a global address to the mobile terminal, which then registers the global address, that is, information on the current location, in a location managing device. The series of operations are called location registration. To transmit a signal, the mobile terminal can directly utilize the global address for communication.
On the other hand, to receive a signal, the terminal in the core network transmits data to the specific address of the mobile terminal. Then, the data is sent to the location managing device, which manages locational information on the mobile terminal. The location managing device changes a header of the data to the global address of the mobile terminal. The location managing device then transfers the data to the mobile terminal. Since mobile terminals and gateway terminals are moved, the mobile terminal executes location registration again when it cannot communicate with the gateway terminal having provided the address to the mobile terminal or when finding a more appropriate gateway terminal.
However, with the above conventional techniques, when the mobile terminal or the gateway terminal is frequently moved, there disadvantageously occurs an increase in the number of signals (referred to as “location registration signals” below) transmitted which allow the registration of data indicating which gateway terminal masters the mobile terminal. This problem will be described with reference to FIG. 23. As shown in this figure, gateway terminals G1 to G4 are present within reach of an electric wave from a base station device BS provided to construct a cellular network cnet. An ad hoc network is formed of the gateway terminals G1 to G4 and mobile terminals (referred to as slave terminals below) mastered by the respective gateway terminals G1 to G4. The ad hoc network is connected to the cellular network cnet, which can be connected to the Internet inet.
Each of the gateway terminals G1 to G4, present within reach of an electric wave from the base station device BS, has a function for cellular communication. Each of the gateway terminals G1 to G4 stores its terminal ID in an HLR (Home Location Register; not shown) in the cellular network cnet in association with its cellular location registration area information. Thus, if there is an incoming message for any of the gateway terminals, the contents stored in the HLR are referenced. The incoming message is then sent to the relevant base station device. Further, the base station device sends the incoming message to the gateway terminal.
On the other hand, the slave terminals do not have the function for cellular communication. Consequently, the slave terminals cannot be connected directly to the cellular network cnet or to the Internet inet. Thus, each of the slave terminals connects to the cellular network cnet via the gateway terminal forming an ad hoc network together with the slave terminal. The connection via the gateway terminal enables the slave terminal to connect to the cellular network cnet and to the Internet inet. This also applies to slave terminals which have the cellular function but which are located beyond reach of an electric wave from the base station device BS; these slave terminals can be connected to both cellular network cnet and Internet inet via the gateway terminal.
The terminal ID of each mobile terminal is stored in an HA (HomeAgent) 10 connected to the Internet inet in association with the location registration area information on the mobile terminal. If there is an incoming message for any of the slave terminals, the contents stored in the HA 10 are referenced. The incoming message is then-sent to the relevant base station device. Further, the base station device sends the incoming message to the gateway terminal. Then, the gateway terminal transmits the incoming message to the slave terminal (as shown by a broken arrow in the figure). When the terminal ID of each slave terminal is always stored in the HA 10 in association with the location registration area information on the mobile terminal, incoming message processing can be executed on the slave terminal regardless of which gateway terminal forms an ad hoc network together with the slave terminal.
The terminal ID of the slave terminal may be stored in the HLR instead of the HA in association with the location registration area information on the slave terminal. Then, if there is an incoming message based on speech communication for the slave terminal, referencing the contents stored in the HLR allows the base station device to transmit the incoming message to the gateway terminal mastering the slave terminal. Then, by transmitting the incoming message from the gateway terminal to the slave terminal, it is possible to execute incoming message processing on speech communication via the gateway terminal.
In this case, when the mobile terminal M moves, it sequentially crosses the location registration areas. Every time the mobile terminal M crosses the location registration area, it transmits a location registration signal to the HA 10 via the gateway terminal (as shown by a solid arrow in the figure). The location registration area is narrower than the reach of an electric wave from the base station device BS. This increases the number of location registration signals transmitted.
The present invention is made to solve the above problems of the prior art. It is an object of the present invention to provide a method for controlling communication, a method for controlling a terminal, a communication control device, a gateway terminal, and a mobile terminal all of which can reduce the number of location registration signals transmitted by the slave terminals of the gateway terminals.